Normal human speech makes use of expired air from the lungs flowing up through the trachea and the larynx to vibrate the vocal cords in the larynx. As a result of disease it is sometimes necessary to remove by surgery a portion of the trachea which may include the larynx (laryngectomy).
Since the larynx normally serves also to prevent contamination of the lungs by oesophageal contents, the passage between the trachea and the pharyngeal oesophagus must be blocked. Consequently at laryngectomy an opening, or stoma, is created to the outside of the throat at the base of the patients neck to which the trachea is permanently diverted. In such patients breathing is then through this tracheostoma.
To restore vocal function it becomes necessary to provide alternative sound producing apparatus as a substitute for the vocal cords. For example it is possible during the surgical procedure to open a fistula between oesophagus and trachea allowing the passage of air into the oral cavity and into which a voice prosthesis, for example in the form of a cylindrically shaped, one-way valve is inserted into this tracheo-oesophagal passageway, is fixed. In any event, to restore vocal function in a patient with a tracheostoma it will be necessary for the tracheostoma to be blocked to allow the patient to force air into the area above the stoma and thus induce vibrations to produce the basis for an acceptable and audible voice.
It is necessary therefore that the tracheotomy patient is able to occlude the stoma when speaking. Most simply this can be done by covering the stoma for example by one or more fingers. However, this is not always practical or pleasant, particularly given that the stoma often is coated by secretion and can have an irregular shape.
More preferably, the stoma is occluded by a manually operated valve. This can be. However it is also known to provide tracheostoma valves which operate automatically. These have a movable closure resiliently biased to an open position. In such a device valve closure pressures are such that normal vegetative breathing pressure is insufficient to move the closure to a closed position and the patient may readily inhale and exhale normally. Speech, however, is initiated at somewhat higher pressure levels. The closure is adapted so that these higher pressures move the valve to a closed position, blocking the free discharge of exhaled air out of the stoma. The air can thus be diverted through a voice prosthesis to produce sound that can be shaped into acceptable speech.
Prior art devices typically include a movable closure, such as a movable diaphragm, contained within a cannular portion inserted into the stoma. This is moveable between an open position for normal breathing and a closed position where the stoma is occluded for speech and is biased to the open position for example by a biasing spring. An accelerating flow of air initiates closing of the valve for speech.
Two further refinements are known. First, a further “cough” valve is often provided as a safety feature closed at normal and speaking pressures but whereby very high pressures cause this to open. For example, where the closure member is slideable in a cannulus, this can be provided at the sides thereof. Second, with different patients and changing exertion and respiration levels, no single closure can have the correct mechanical characteristics to work ideally in all situations, and some prior art valves are adjustable, for example by means of a screw thread setting distance between open and closed position and/or the exchanging of interchangeable springs biasing the valve to alter the closure pressure, to allow this to be changed by the patient.
Embodiments of such valves illustrating some or all of these features are disclosed for example in U.S. Pat. Nos. 4,582,058, 5,059,208, 5,738,095, and 6,193,751.
These prior art devices all have complex multi-component mechanisms. This can raise costs, increase the possibility of malfunctions, and in particular make the tracheostoma valves difficult to operate and keep clean. This last point can be a particular problem. The valves can easily become contaminated with mucus from the trachea and/or with dust and like contaminants from outside. This can effect the efficiency not only of the functioning of the valve but also of the general functioning of the stoma itself. This is a particular problem in patients who have had a laryngectomy, since the procedure itself tends to lead to an increase in mucus production.
Furthermore, it is frequently desirable to provide for a filter in the stoma, for example to serve as a means to keep external contaminants out of the trachea, as a means in part to normalise conditions within the trachea, in particular heat-moisture, as a means to control air flow resistance during normal breathing etc, to protect the stoma, or simply for cosmetic purposes. Not all prior art devices are compatible for use with such prior art stoma filters, such as heat-moisture exchange (HME) filters.